NABLUS, West Bank, 25 June — A Palestinian activist said to be wanted by Israel was killed in a West Bank bomb blast yesterday, signaling Israel may have abandoned a US-brokered cease-fire that was already on the verge of collapse. The blast occurred as the hawkish Israeli Prime Minister Ariel Sharon left for the United States, where he is expected to tell President George W. Bush that Israel cannot keep up the truce indefinitely in the face of continued violence.

Osama Fathi Jawabra, a 29-year-old member of Palestinian President Yasser Arafat’s Fatah faction, was killed when a public telephone booth he was using in Nablus exploded. Fatah accused Israel of assassinating Jawabra.

An official aboard Sharon’s US-bound plane said the Palestinians had been given a list of several dozen “terrorists” at the weekend to be arrested and that the Palestinian Authority had failed to do so. He warned: “We demand a 100 percent halt to the violence. Otherwise, there will not be any passage to the next stage” in restarting peace negotiations.

US and European diplomats have been pushing to hold together the cease-fire accord, which itself was an attempt to get rolling the wider recommendations of the Mitchell Commission aimed at getting the two sides back to peace talks.

US envoy William Burns said after talks with Egyptian President Hosni Mubarak in Cairo that there was an “urgent need” for further steps to stabilize the truce as well as measures to improve life for despairing Palestinians.

“It’s not an easy task but it’s one that is very important for the parties themselves as well as the United States and Egypt,” and others, said Burns, who had met with Arafat on Saturday.